The present invention relates to the use of certain types of proppants in fracturing subterranean formations and to advanced methods of fracturing with proppants. The present invention further relates to the use of proppants for hydrocarbon recovery.
Proppants are materials pumped into oil or gas wells at extreme pressure in a carrier solution (typically brine) during the hydrofracturing process. Once the pumping-induced pressure is removed, proppants “prop” open fractures in the rock formation and thus preclude the fracture from closing. As a result, the amount of formation surface area exposed to the well bore is increased, enhancing recovery rates.
Ceramic proppants are widely used as propping agents to maintain permeability in oil and gas formations. High strength ceramic proppants have been used in the hydrofracture of subterranean earth in order to improve production of natural gas and/or oil. For wells that are drilled 10,000 feet or deeper into the earth, the proppant beads need to withstand 10 kpsi or higher pressure to be effective to prop the fracture generated by the hydrofracture process. Currently only proppants formed from high strength materials, such as sintered bauxite and alumina have sufficient compressive and flexural strength for use in deep wells. These conventional high strength materials are expensive, however, because of a limited supply of raw materials, a high requirement for purity, and the complex nature of the manufacturing process. In addition, such high strength materials have high specific gravity, in excess of 3.0, which is highly undesirable for proppant applications. Producing high strength proppants with low specific gravity is also a challenge. In field applications, the transportability of proppants in wells is hindered by the difference of specific gravities of proppant and carrying fluid. While light weight oxide materials, such as cordierite, have low specific gravity, they have a relatively weak flexural strength and stiffness.
While ceramic proppants have been known, the previous ceramic proppants that are considered conventional had numerous defects and inconsistencies. For instance, as can be seen in FIGS. 21 and 22, conventional proppants were not uniform in shape or in surface characteristics. This is further confirmed by various ceramic proppants previously described or commercially available. For instance, FIGS. 26-31 provide images of various conventional ceramic proppants, and, as can be seen from these images, the surface of the proppants had numerous defects with regard to irregular and inconsistent shapes, irregular and inconsistent sizes, or surface defects. Each of these negative attributes would lead to inconsistent proppant performance when injected into a well and most especially would lead to proppant failure at a low crush strength.
While there is literature that describes nearly-monodispersed proppants and other references that characterize particles or proppants as monodispersed, there is a problem with such characterizations. First, no quantified descriptions are given when the term “monodispersed” is used to characterize particles of proppants. Thus, the monodispersity may have an immense distribution area involved, such that the standard deviation is over five standard deviations. No effort has been made in most, if not all, of this literature to quantify the monodispersity. Further, based on the methods described in these various literature articles, it would appear that achieving a highly-monodispersed proppant population would not be possible and that the standard deviation would be significant.
In addition, while various methods can be used to make proppants, and then classification techniques can be used to achieve some standard sizing, it is important to point out the following. Standard screen or sieve classifications will have typically a deviation or error of ±100 microns, for instance. The coefficient of variation for screen or sieve classification is over 20 to 25% or higher, whereas the coefficient of variation for air classification methods would be a coefficient of variation of 10 to 15% or higher. None of these techniques would produce a proppant population of monodispersity and further would not create a proppant population with a 3-sigma distribution with the width of the total distribution being more than 5% of the mean particle size.
A previous filing by the same assignee developed novel and effective proppants that are highly monodispersed. The inventors here have now discovered that using the highly monodispersed proppants in certain ways provides effective means to better control fracturing and/or increase hydrocarbon recovery and/or provide the ability to reduce the amount of proppant and yet achieve comparable recovery rates.